The female breast is composed predominantly of fatty tissue. Lacking overlying muscle, the breast is supported by skin and ligaments. Such supporting skin and ligaments are readily stretched and further gradually lose elasticity as part of the normal aging process.
Additional support for the breast may be provided by a brassiere (bra). While a general use or "everyday" bra provides adequate support for more sedate or non-athletic activities, such bras fail to provide the support needed during vigorous activity, such as running, aerobics or the like. Such activities may generate substantial forces that tend to impart vertical and/or lateral components of motion to the breasts. Aside from causing discomfort and pain, such motion can accelerate and exacerbate the stretching of skin and ligaments, resulting in sagging of the breasts. The larger the breast, the more acute the problem is likely to be. To address the increased support requirements occasioned by vigorous exercise, the sports or exercise bra was developed.
The sports bra is intended to restrain the breasts from moving in response to the aforementioned forces, yet must provide freedom of movement and comfort to the wearer. Current sports bra designs are based on at least one of two underlying design principles: encapsulation and compression. Encapsulation bras seek to firmly and individually confine each breast within a cup-like structure. Compression bras force the breasts against the chest as a single mass. Compression bras are likely to be more suitable for smaller- rather than larger-breasted women.
A wide variety of sports bras are currently available. It is expected that some of such bras provide satisfactory support for smaller-breasted women engaging in vigorous activity. Current sports bras are, however, of dubious value for meeting the needs of larger-breasted women engaging in such vigorous activity.